JP2002321216A - Method for manufacturing crosslinked fluoroplastic sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a crosslinked fluoroplastic sheet capable of performing homogeneous crosslinking work with high work efficiency. SOLUTION: The single surface of a running fluoroplastic sheet 42 is brought into contact with a uniformly heating member 24 to hold the fluoroplastic sheet 42 to a predetermined temperature and the other surface of the fluoroplastic sheet 42 is irradiated with radiation in this state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked fluororesin sheet, and more particularly to a method for producing a crosslinked fluororesin sheet capable of performing a uniform crosslinking operation with high working efficiency.

[0002]

2. Description of the Related Art In order to improve the properties such as the strength and elongation of a fluororesin sheet, radiation is applied to crosslink the molecules of the fluororesin constituting the sheet.

FIG. 3A summarizes a sheet manufacturing procedure based on irradiation of a fluororesin powder with radiation.
First, the unfired powder of the fluororesin as a raw material is supplied to a fixed mat mold, which is then fired by heating it to a temperature equal to or higher than its melting point. The process is repeated by subjecting the mixture to a cross-linking process of repeatedly performing cooling and pulverization to return the powder to a powder, and then processing this into a sheet.

[0004] FIG. 3 (b) shows the above procedure.
The outline of the equipment used in the crosslinking process of
Denotes an electron beam irradiation device, 2 denotes an irradiation chamber installed below the irradiation device 1 through an irradiation window 3, 4 denotes a carrier arranged to circulate in the irradiation room 2, and a conveyor 5 and It is composed of trays 6 suspended at regular intervals.

A fired body 7 of a fluororesin powder solidified in a mat shape is placed on the tray 6, and the fired body 7 is irradiated with an electron beam every time it passes under the irradiation window 3. The interior of the irradiation chamber 2 is set at a temperature slightly higher than the melting point of the fluororesin by circulation of heated nitrogen gas, and is placed in an oxygen-free state by this nitrogen gas to eliminate the influence of oxygen. Further, the irradiated fired body 7 is cooled to the original temperature by circulation of nitrogen gas,
This is set so that a crosslinking temperature of ± 10 ° C. is maintained.

FIG. 4 shows a method of directly producing a crosslinked fluororesin sheet without passing through a powder fired body as shown in FIG. 3, and this method is used when a thin solid sheet is to be crosslinked. Applied. The uncrosslinked fluororesin sheet 9 is drawn out from the reel 8 and drawn into the heating chamber 10, where it is heated to the crosslink temperature.
The work is advanced by winding it up.

A high-temperature nitrogen gas is forcibly circulated through the heating chamber 10 and the irradiation chamber 11, thereby heating the sheet 9 before crosslinking to a predetermined crosslinking temperature, and raising the sheet 9 by electron beam irradiation. Conditions are set such that temperature fluctuation due to temperature is suppressed, and a uniform crosslinking is obtained while maintaining a crosslinking temperature of ± 10 ° C.

The former method is characterized in that the fired body 7 is irradiated with an electron beam each time it passes through the position of the irradiation window 3 to accumulate the dose, thereby performing a predetermined crosslinking. On the other hand, the latter method is characterized in that crosslinking is performed by one pass. All of these methods, which can be selectively used depending on the thickness of the cross-linking target, have a proven track record as methods suitable for the production of cross-linked fluororesin sheets, and have been appropriately evaluated and utilized.

[0009]

However, according to the conventional method for producing a crosslinked fluororesin sheet, in the former method, even if an irradiation apparatus having an acceleration voltage of 800 keV class is used, the electron beam in the irradiation object is not used. In view of the relationship with the effective range, the maximum thickness of the fired body 7 that can be applied is limited to 3 mm, and the bulk density of the fired body 7 is set to 0.5 to 0 in order to facilitate pulverization after crosslinking. As a result, the weight or volume of the fired body 7 is naturally restricted.

In addition to this, in this method, in order to adjust the temperature for maintaining the cross-linking temperature, it is usual that the conveying speed of the fired body 7 is restricted, and therefore, due to the above factors, However, the working efficiency of this method must be extremely low, and the temperature adjustment by circulating nitrogen gas has a limit in accuracy, so that the obtained cross-linked state often varies.

On the other hand, the latter method is efficient because the crosslinking can be performed in one pass, but the former method is less efficient in that the heat generated from the sheet due to electron beam irradiation is cooled by circulating nitrogen gas. The same, therefore, in order to maintain the crosslinking temperature, it is necessary to suppress the traveling speed of the sheet,
Similarly, the work efficiency is lowered, and the temperature control accuracy is poor due to the circulation of the nitrogen gas.

Accordingly, it is an object of the present invention to provide a method for producing a crosslinked fluororesin sheet capable of performing a uniform crosslinking operation with high working efficiency.

[0013]

Means for Solving the Problems In order to achieve the above object, the present invention provides a method for producing a crosslinked fluororesin sheet, which comprises irradiating a fluororesin sheet with radiation to crosslink the molecules of the fluororesin sheet. One side of the running fluororesin sheet is brought into contact with the heat equalizing member, and the other surface of the fluororesin sheet is irradiated with radiation of a predetermined dose while the fluororesin sheet is maintained at a predetermined temperature by the heat equalizing member. And a method for producing a crosslinked fluororesin sheet.

The above-mentioned fluororesin sheet may be either a solid sheet or a sheet-like fired powder which is pulverized after crosslinking. Further, it is preferable that the heat equalizing member has a small heat fluctuation and a large heat capacity as much as possible in order to eliminate the influence of temperature rise due to radiation irradiation in a short time. As the radiation, ionizing radiation such as an electron beam is preferable because it is easy to handle.

As the heat equalizing member, a heat equalizer using an electric heater or steam as a heat source can be used. However, a working fluid capable of evaporating and condensing is supplied to the internal space to form a liquid film on the inner wall surface. Use of a heat siphon type soaker that forms and supplies an appropriate amount of working fluid to the inside and discharges the amount of working fluid corresponding to the supply amount to the outside to keep the internal vapor pressure constant at all times. When such a configuration is adopted, heat absorbed by the heat equalizing member from the fluororesin sheet can be efficiently discharged to the outside of the system, and uniform cross-linking work without temperature fluctuation of the fluororesin sheet can be performed. It becomes possible. As the working fluid, “Dowtherm A” (eutectic mixture of biphenyl and diphenyl oxide) or the like is suitable.

As the shape of the heat equalizing member, a rotary roll type or a flat plate with a flat surface can be considered. In particular, the former roll type shape allows the running fluororesin sheet to have a gap under an appropriate tension. Because it has the characteristic to make it adhere without
Contact heat resistance can be minimized, and an advantageous state can be created for maintaining the temperature of the fluororesin sheet. In addition, the roll-type shape is advantageous for increasing the contact area by increasing the contact angle, so that it is possible to reliably control the temperature and obtain the effect of improving the efficiency by increasing the contact area. Can be.

[0017]

Next, an embodiment of a method for producing a crosslinked fluororesin sheet according to the present invention will be described. In FIG. 1A, 21 is an electron beam irradiation device, 22 is an irradiation room provided at a lower position thereof, 23 is an irradiation window formed on a ceiling of the irradiation room 22, and 24 is provided in the irradiation room 22. 3 shows a heat equalizing member.

FIG. 1B shows the structure of the heat equalizing member 24 and its accompanying equipment.
And has a flat plate shape having wicks 27 for ensuring wettability on the upper and lower inner wall surfaces, and is configured to receive heat when installed on a heater 28. I have. Reference numeral 29 denotes a fluid tank connected to one end of the heat equalizing member 24 by a pipe 30, and supplies a working fluid 31 to the internal space 26 of the heat equalizing member 24. Reference numeral 32 denotes a pump for performing the supply. .

Reference numeral 33 denotes an automatic temperature control type heater wound around the fluid tank 29 to heat the working fluid 31, and reference numeral 34 denotes a heat insulating material. The working fluid 31 is always kept at a constant temperature by these configurations. I have. 35 is a constant pressure valve connected to the other end of the heat equalizing member 24, 36 is a condenser for condensing the working fluid vapor sent through the constant pressure valve 35, and the condensed working fluid is returned by the pump 37. The fluid tank 29 is connected to the fluid tank 29 by a pipe 38 as described above.

The pressure in the internal space 26 of the heat equalizing member 24 is
The supply amount of the working fluid 31 by the pump 32 and the heater 28
The temperature of the heat equalizing member 24 is also maintained constant, as a result of maintaining the balance with the discharge amount of the working fluid 31 vaporized by the heat from the constant pressure valve 35 as a result. I have.

Therefore, the heat equalizing member 24 has a temperature maintaining property which is hardly affected by others, and if the contact material to the surface thereof is a sheet-like material having a small heat capacity, it can be easily replaced by its own. It can be adjusted to the temperature level. In the drawing, reference numeral 39 denotes a vacuum pump for discharging the non-condensable gas outside the station.

Returning to FIG. 1A, reference numeral 40 denotes the irradiation chamber 22.
A heating chamber 41 provided on the inlet side for preheating the material, 41 is a conveyor for drawing the fluororesin sheet 42 into the heating chamber 40, and 43 is irradiated with a predetermined dose of electron beam in the irradiation chamber 22 and crosslinked. A cooling chamber 44 for cooling the sheet 42 is a conveyor provided in the cooling chamber 43.

The crosslinking in this embodiment is performed under the following conditions. That is, polytetrafluoroethylene (P
When TFE) is applied, the temperature of the heat equalizing member 24 becomes PT
When the temperature is set to 340 ° C., which is the cross-linking temperature of the FE, and when Dowtherm A is used as the working fluid 31, the pressure of the constant pressure valve 35 is set to 464 kPa.

On the other hand, the total energy amount of the electron beam irradiated from the irradiation device 21, for example, the total energy amount of about 600 W in consideration of the attenuation at an acceleration voltage of 800 kV and a current value of 1 mA is converted into heat. Assuming that
In order to extract the total amount of energy in this case with the vapor of the working fluid 31 and absorb it in the condenser 36,
The required circulation amount of the working fluid (Dowtherm A) 31 is such that the latent heat of evaporation and condensation at a crosslinking temperature of 340 ° C.
Therefore, about 0.15 kg / min (190 c
m3 / min).

Therefore, the heat equalizing member 2 is
4 is set to 340 ° C., and one side of the sheet 42 is brought into contact with the sheet 42 for traveling, and the other side of the sheet 42 is irradiated with an electron beam having a total energy amount of 600 W. The heat is effectively absorbed by the heat member 24, so that a uniform crosslinking operation can be performed without being affected by the temperature rise.

Moreover, unlike the conventional convection cooling by circulation of nitrogen gas or the like, the temperature of the fluororesin sheet 42 is adjusted by contact with the heat equalizing member 24, so that the temperature control action is direct. , And thus the sheet 42
Therefore, it is possible to increase the running speed and increase the irradiation amount of the electron beam, so that the work can be performed with high efficiency. The heat resistance in the case of cooling by the conventional nitrogen gas circulation is about 0.024 m 2 K / W at a practical circulation speed, whereas in the case of the present invention by direct contact with the heat equalizing member 24, Obviously, an order of magnitude lower thermal resistance level is obtained, and thus the above-mentioned homogeneous crosslinking and high-efficiency operation are fully ensured.

A nitrogen gas heated to a temperature slightly lower than the crosslinking temperature is forcibly circulated in the irradiation chamber 22, the heating chamber 40, and the cooling chamber 43, so that the crosslinking is not affected by oxygen. An atmosphere is formed. Circulating an inert gas such as nitrogen gas cools the electron beam irradiation side of the fluororesin sheet 42 and contributes to suppressing the temperature rise, and also absorbs a part of the heat conversion amount of the electron beam. Therefore, this is a preferable mode for the present invention.

FIG. 2 shows another embodiment of the method for producing a crosslinked fluororesin sheet according to the present invention. The difference from FIG. 1 is that the heat equalizing member 24 is constituted by a roll type. Others are the same including the working conditions (the same reference numerals as those in FIG. 1 indicate the same parts as those in FIG. 1).

As shown in FIG. 2B, a universal joint 45 is attached to one shaft of the roll type heat equalizing member 24, and a pipe 46 extended from the pipe 30 through the universal joint 45. Are arranged inside the heat equalizing member 24, and the working fluid 31 is supplied from the nozzle 47.

A wick 27 is formed on the inner surface of the heat equalizing member 24 in the circumferential direction, so that the entire inner surface of the heat equalizing member 24 is easily wetted by the working fluid 31. Reference numeral 48 denotes a universal joint attached to the other shaft of the heat equalizing member 24, and the steam of the working fluid 31 discharged from this is sent to the condenser 36 through the constant pressure valve 35, condensed and returned to the tank 29. It is configured to be.

In the case of this embodiment, the heat equalizing member 24
Is a roll type, so that the contact area between the heat equalizing member 24 and the fluororesin sheet 42 can be increased, and therefore, the high temperature maintaining property for the fluororesin sheet 42 allows more uniform crosslinking work and Thus, highly efficient work can be performed based on an increase in irradiation amount and an increase in traveling speed.

[0032]

As described above, according to the method for producing a crosslinked fluororesin sheet of the present invention, one side of a running fluororesin sheet is brought into contact with a heat equalizing member to maintain a predetermined temperature level. Since the cross-linking is performed by irradiating the other surface of the fluororesin sheet with radiation, it is possible to maintain a reliable sheet temperature by contact of the heat equalizing member. High-efficiency work can be realized by increasing the amount and traveling speed.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing an embodiment of a method for producing a crosslinked fluororesin sheet according to the present invention, wherein (a) is a schematic view of an apparatus used, and (b) is a heat equalizing member and auxiliary equipment thereof. The details are shown below.

FIGS. 2A and 2B are explanatory views showing another embodiment of the method for producing a crosslinked fluororesin sheet according to the present invention, wherein FIG. 2A is a schematic diagram of an apparatus used, and FIG. The details of the ancillary equipment are shown.

3A and 3B are explanatory views showing a conventional method for producing a crosslinked fluororesin sheet, wherein FIG. 3A shows the procedure, FIG. 3B shows an outline of an apparatus used, FIG. 3I shows a front view, and FIG. Shows a side view.

FIG. 4 is an explanatory view showing another conventional method for producing a crosslinked fluororesin sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Electron beam irradiation apparatus 22 Irradiation room 23 Irradiation window 24 Heat equalizing member 25 Rib 26 Internal space 27 Wick 28 Heater 29 Fluid tank 30, 38 Piping 31 Working fluid 32, 37 Pump 33 Electric heater 34 Insulation material 35 Constant pressure valve 36 Capacitor 39 Vacuum pump 40 Heating chamber 41, 44 Conveyor 42 Fluororesin sheet 43 Cooling chamber 45, 48 Universal joint 46 Pipe 47 Nozzle

Claims (3)

[Claims] In a method for producing a crosslinked fluororesin sheet, wherein the fluororesin sheet is irradiated with radiation to crosslink the molecules of the fluororesin sheet, one side of the running fluororesin sheet is brought into contact with a heat equalizing member, A method of manufacturing a crosslinked fluororesin sheet, comprising irradiating a predetermined dose of radiation to the other surface of the fluororesin sheet while maintaining the fluororesin sheet at a predetermined temperature by the heat equalizing member. 2. The step of maintaining the fluororesin sheet at a predetermined temperature by the heat equalizing member includes forming a liquid film of a working fluid capable of evaporating and condensing on an inner wall surface, and internally forming the working fluid of the working fluid. A heat equalizer that receives the supply and discharges the vapor amount of the working fluid corresponding to the supply amount to the outside so as to always maintain the internal vapor pressure corresponding to the set temperature is used as the heat equalizing member. The method for producing a crosslinked fluororesin sheet according to claim 1, wherein 3. The step of maintaining the fluororesin sheet at a predetermined temperature by the soaking member is performed by using a rotating roll type soaking member as the soaking member. Item 4. The method for producing a crosslinked fluororesin sheet according to Item 1.